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Howard Marks
Howard Marks
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Scale-up, Scale-Out Nexsan Blurs the Line

In the beginning, or at least the 20th century, modular scale-up storage systems dominated the market for midrange storage. More recently, the vendors of scale-out systems for NAS and iSCSI have touted the way their systems add controller horsepower and cache as they add capacity. Nexsan's new NST line of unified storage systems combines attributes of both architectures, hoping to leverage the best of both worlds.

In the beginning, or at least the 20th century, modular scale-up storage systems dominated the market for midrange storage. More recently, the vendors of scale-out systems for NAS and iSCSI have touted the way their systems add controller horsepower and cache as they add capacity. Nexsan's new NST line of unified storage systems combines attributes of both architectures, hoping to leverage the best of both worlds.

The problem with scale-up systems is that any given model controller has a limited range of scalability. A typical system will have a pair of redundant controllers connected to several shelves of disk drives through a limited number of Fibre Channel loops or, more recently, switched SAS ports. As disk shelves are added to the system, they have to share the limited back-end bandwidth from controllers to drives.

Each small write to a RAID set generates several times as much traffic on the back end of an array between the controller(s) and disk shelves as was received on the front end from the host. This is because the system has to read from multiple drives to generate new parity data. So, limited back-end bandwidth, and controller CPU cycles for parity calculations, limits any given controller's capacity to run disk drives.

Scale-out systems avoid this problem by delivering drives and controllers in a single package. Each time a customer adds an EqualLogic or Isilon node to their system, they're adding more controller horsepower as well as capacity. The downside to scale-out is that capacity has to be added a whole node at a time, and since each node is a full featured storage system, each node is more expensive than a dumb JBOD.

Nexsan's NST systems use a storage bridge bay cabinet to manage file and iSCSI access to its internal bays, which can hold spinning disks or SSDs to use as cache, and for the larger models, Nexsan's E-Series Fibre Channel RAID arrays. This architecture reduces the traffic on the back-end Fibre Channel network and offloads basic RAID functions without the complications of managing access, snapshots and other sophisticated features in every node of a scale-out system. While the E-Series systems aren't the most feature-rich RAID arrays on the market, the high-density (60 drives) E-60 is a leader in energy efficiency using Nexsan's multilevel AutoMAID to spin down idle drives.

The combination of a NAS head and RAID array has gotten a bad rap because most earlier systems required the administrator to manage disk drives and RAID operations through one user interface, and NAS or iSCSI access through another. Nexsan's built a unified management engine into the NST that manages both the NST and the back-end E-series.

Nexsan is not a client of DeepStorage, Llc.

Howard Marks is founder and chief scientist at Deepstorage LLC, a storage consultancy and independent test lab based in Santa Fe, N.M. and concentrating on storage and data center networking. In more than 25 years of consulting, Marks has designed and implemented storage ... View Full Bio
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